In a Power BI semantic model, which storage mode should aggregated tables use?

• A. Dual mode
• B. Import mode
• C. DirectQuery mode
• D. None

Answer: (B)

Aggregated tables are pre-aggregated data sets used to speed up queries over large fact tables. In a Power BI semantic model, these tables should be stored in Import mode. Loading the aggregated data into the in-memory engine (VertiPaq) gives fast, predictable performance because the engine can quickly scan and combine pre-aggregated results without repeatedly querying the source. This makes the dataset self-contained and refreshable, ensuring consistent results and quicker responses for common aggregations.

DirectQuery would keep the aggregated data on the source and push queries back to it, which undermines the purpose of having pre-aggregated results and can lead to slower performance and dependency on source-side efficiency. Dual mode introduces complexity by allowing both in-memory and live query paths, which can cause inconsistent behavior for the aggregates. Therefore Import mode is the best fit for aggregated tables.